Michael A. Keller

Oxidative stability and degradation mechanism of a cyclotriphosphazene lubricant.

Chromatographic and spectroscopic techniques were used to investigate the degradation products from bulk oxidative and thermal stability testing of a substituted tricyclophosphazene high-temperature lubricant. Analytical investigation into the degraded lubricant revealed oligomerization to be the dominant mode of degradation, resulting in most of the observed viscosity increases. GC/MS, FT-IR, and (31)P NMR data confirmed the existence of a cyclotetramer structure in the degraded fluid, while GPC analysis indicated the possibility of a much smaller amount of higher oligomers. The poor reproducibility observed for the oxidation results is likely due to the influence of trace contaminants or the relative degree of retention of ionizable volatile products that could act as oligomerization catalysts.

Behavior of high temperature lubricants in a pressure differential scanning calorimeter

The effects of pressure and diffusion restriction on pressurized differential scanning calorimetry (PDSC) data were investigated for several classes of high temperature lubricants, including polyphenylethers, polyphenylthioethers, cyclophosphazenes and perfluoroalkylethers. Unlike conventional lubricants, such as mineral oils and synthetics like ester-based lubricants, appreciable oxidation only occurs when both diffusion restriction and high pressure exist. This was shown to be due to a reduction in the rate of weight loss of the lubricant and, although not shown, is also probably due to oxygen saturation of the liquid phase. The onset of the exotherm and the onset of extreme degradation for these lubricants correlated for polyphenylethers and polyphenylthioethers but not for the cyclophosphazene. Perfluoroalkylethers display very small exotherms which are very likely due to their unusually high stability and scissioning degradation mechanism.

Characterization of higher molecular weight oxidation products of formulated and unformulated polyphenyl ethers

Abstract The analysis of higher molecular weight oxidation products of a bis(phenoxy phenoxy)benzene (5P4E) polyphenyl ether lubricant is reported. The oxidation of polyphenyl ether at 320°C results in the formation of products that cause large kinematic viscosity increases. Analyses by solvent fractionation and gel permeation chromatography reveal these products to consist of a dimer (HMW-1) and higher molecular weight compounds (HMW-2) that were too complex to be completely characterized. Two proprietary additives were observed to be very effective in reducing the rate of formation of these higher molecular weight compounds. While the first additive effectively slowed the rate of formation of both HMW-1 and HMW-2, the second additive completely inhibited the formation of HMW-2 and thus was a more effective antioxidant. Evidence is shown to suggest that the instability of HMW-2 results in an acceleration of polyphenyl ether oxidation.

Monitoring of Polyphenyl Ether Lubricants Using Fluorescence Spectroscopy

Fluorescence spectroscopy has been investigated to determine its suitability for condition monitoring of oxidized polyphenyl ether lubricants. Oxidative degradation of the lubricant was shown to induce specific changes in its fluorescence properties. Excitation/emission wavelengths with monitoring potential were identified and were found to yield a useful correlation between emission intensity and viscosity increases of the degraded lubricant for two different formulations. Application of this technique on neat thin films of the degraded fluids yields similar correlations.

Gas Chromatographic Monitoring of Hydroxyl Components in Oxidized Turbine Engine Lubricants

Changes in levels of hydroxyl compounds in synthetic ester based turbine engine lubricants were measured by derivatization and detection by gas chromatography with an atomic emission detector. Conversion of hydroxyl groups to trifluoracetates were made with the acetylating agent N-methylbis[trifluoroacetamide]. Although individual hydroxyl compounds could be quantified by gas chromatography, total hydroxyl content was most accurately measured by the quantity of the reaction byproduct, N-methyl trifluoroacetamide. Analyses of field samples showed a good relationship between elevations in hydroxyl numbers and deposition problems and were more reliable than COBRA, TAN and conductivity values. A good correlation was also noted between deposition in a dynamic coking apparatus and hydroxyl number increases. Analyses of corrosion and oxidation tested lubricants reveals relatively smaller increases in hydroxyl number despite large increases in degradation levels.

Catalytic Degradation of a Perfluoroalkylether in a Thermogravimetric Analyzer

Catalytic degradation of perfluoroalkylethers (PFAEs) by various substrates can be a significant problem, resulting in the formation of corrosive degradation products and loss of lubricant. The determination of catalytic degradation of a linear PFAE (PFAE-D) by various substrates was made by controlled-diffusion thermogravimetric analysis. The use of a sealed gold pan with a small pinhole in the lid allowed for the measurement of catalytic degradation of PFAE-D by increases in the rate of volatilization relative to a control. Catalytic degradation was observed under ramped conditions (to 500°C) for most commonly used metals and alloys except Inconel 600, silver and pure silicon nitride. Analysis of degradation products confirmed that degradation was occurring by a molecular disproportionation reaction. Milder isothermal conditions (300° C) resulted in catalytic degradation for aluminum, M-50 steel, carbon-carbon composite and some binder components used in silicon nitride balls. Presented at the 53rd Annu...

Chromatographic analysis of phenyl-1-naphthylamine and 4,4′-dioctyldiphenylamine and their intermediate oxidation products in oxidized lubricants

Abstract The quantitative analysis of two secondary aromatic amine antioxidants, phenyl-1-naphthylamine (PANA) and 4,4′-dioctyldiphenylamine (DODPA), by gas chromatography (GC) with a thermionic specific detector is described. Isolation of the oxidized products of these amines in an oxidized lubricant by liquid chromatography, their subsequent identification by mass spectrometry and their semi-quantitative analysis by GC with a thermionic detector is described. Quantitative analysis data of these compounds in lubricants formulated with PANA and DODPA during thermal and oxidative laboratory tests is presented.

Characterization of friction polymer from wear testing of polyphenyl ethers

Abstract The characterization of friction polymer generated during sliding four-ball testing of polyphenyl ether with 52100 and M50 steel balls is reported. The organic fraction was shown by Fourier transform infrared spectroscopy to consist of organic solvent insoluble, oxidized, high molecular weight compounds. Analysis of the metallic portion of the friction polymer indicated levels of iron that were inversely proportional to the test temperature. Friction polymer from M50 steel balls was found to have much higher iron levels than that produced from 52100 steel balls, commensurate with their respective wear rate differences. 57 Fe Mossbauer spectroscopy indicated that virtually all the iron in the friction polymer exists as high-spin Fe(III) for all test temperatures and both ball materials. The lack of significant amounts of metallic iron indicated that corrosive removal of iron is the dominant wear mode under sliding conditions. Friction and wear studies have shown that the friction polymer possesses anti-wear characteristics but no lubricity property.